This invention relates to preservative compositions, and, more particularly, to high purity, clear, light stable, formaldehyde-free preservative compositions containing a compound formed by the reaction of excess glycine and formaldehyde at low temperatures.
P. Berke et al, in U.S. Pat. No. 4,337,269, described a biocidal composition containing the crystalline product obtained from the reaction of glycine and formaldehyde, at a 1:1 molar ratio of reactants. Under these reaction conditions, the product obtained included considerable amounts of free formaldehyde.
Accordingly, it is an object of this invention to provide a high purity, clear, light stable, formaldehyde-free biocidal composition of the reaction product of glycine and formaldehyde, with predetermined amounts of residual glycine therein and substantially no unwanted by-products of the reaction.
These and other objects and features of the invention will be made apparent from the following more detailed description hereinafter.
What is described herein is a high purity, clear, light stable, formaldehyde-free, non-toxic composition for inhibiting growth in a substance requiring microbial inhibition comprising about 40-60% by weight of an aqueous solution of hydroxymethyl aminoacetate in the form of its alkali metal salt which is formed by the reaction of excess glycine, a lower alkyl substituted glycinate, or salts thereof, with formaldehyde, in an aqueous medium, at a pH of about 10.5-12.5, characterized by carrying out the reaction at a molar ratio of glycine to formaldehyde necessary to maintain a molar excess of glycine in the medium and to leave a predetermined amount of residual glycine present in the composition at the conclusion of the reaction, and sufficient to preclude the presence of any detectable free formaldehyde as methylene diol in the resultant composition.
In suitable embodiments of the invention, the reaction between excess glycine and formaldehyde is carried out with a molar excess of glycine of 0.5 to 10% over a 1:1 molar ratio of glycine to formaldehyde; so that no free or residual formaldehyde as methylene diol can remain in the composition at the conclusion of the reaction. The residual excess glycine level in the composition is 750-35,000 ppm, preferably 1000-3000 ppm.
Preferably, the reaction is carried out at a temperature of  less than 40xc2x0 C., most preferably 10-25xc2x0 C., whereat no unwanted by-products can form during the reaction.
The overall chemistry of the reaction herein is given in Equation (A) below: 
However, the reaction product can also undergo a dehydration reaction (B) to produce a Schiff base: 
The Schiff base is a reactive species which can undergo various side reaction which produce unwanted by-products, such as cyclization reactions to form the corresponding lactones, as well as hexahydro-triazines, and polymeric products thereof. These side reactions are minimized herein because the main reaction is carried out at a low temperature, i.e. below 40xc2x0 C. and preferably at about 10-25xc2x0 C. At such low temperatures, formation of the Schiff base in reaction (B) is minimized. Thereby, the resultant reaction composition contains only a minimum amount of undesirable reaction by-products.